Indium tin oxide is known as a transparent conductive material. For example, Patent Document 1 discloses an ITO powder in which a Sn/In ratio is 0.005 to 0.3, a specific surface area (BET value) is 10 m2/g or more, a specific resistance is 70 Ωcm or less, a content of Cl is 0.1% or less, a content of Na and K is 10 ppm or less, and a content of free In and Sn is 10 ppm or less. In addition, Patent Document 2 discloses an ITO powder in which a specific surface area is 4 to 20 m2/g, and a color tone of the powder, L is 82 to 91 in a Lab colorimetric system.
The ITO powder is used as a material for forming a conductive film, an infrared ray shielding layer, or the like. For example, ITO powders are dispersed in a resin to prepare a coating material. This coating material is applied to a substrate to form a conductive film. In the alternative, the coating material is dispersed in a resin to manufacture a film, and this film is adhered onto a substrate to form a conductive film. Or, the film is interposed between laminated glasses to form a conductive layer or an infrared ray shielding layer, In the case of forming this conductive film, it is preferable that the ITO powder be as fine as possible so as to increase transparency of the film.
A specific surface area of the ITO powders disclosed in Patent Documents 1 and 2 is approximately 20 m2/g which is not very large. In view of this, there is known an ITO powder in which a specific surface area is increased so as to increase transparency. For example, Patent Document 3 discloses an ITO powder having a specific surface area of 50 m2/g or more. In addition, Patent Document 4 discloses an ITO powder having a specific surface area of 55 m2/g or more.
On the other hand, there is a tendency that when a primary particle size of the ITO powder decreases, crystallinity thereof decreases and conductivity deteriorates. Therefore, in order to form a film in which the transparency and the conductivity are high, a fine ITO powder is required in which the specific surface area is large and the crystallinity is high,
Here, with regard to the ITO powders disclosed in Patent Documents 3 and 4, the specific surface area is larger than that of a product in the related art, and the ITO powders are finer than that of the product in the related art. However, in a color tone of each of the powders, L is approximately 52 to 90 (a water color to a dilute water color) in a Lab colorimetric system. According to this color tone of the powder, the crystallinity is not so high.